1. Field of the Invention
The present invention relates to a method of detecting gas leaks in pressurized containers, and more particularly to the detection of small gas leaks in an ambient atmosphere which may contain significant quantities of the same gas being detected.
2. Description of the Prior Art
The method of the present invention may be used to detect small gas leaks in any type of container. While not intended to be so limited, for purposes of an exemplary showing, the method will be described in its application to the detection of small propellant leaks in aerosol containers. The method is adaptable to a continuous in-line testing system in an aerosol container filling line or the like. However, again for purposes of an exemplary showing, the method will be described in terms of a batch-testing system.
All aerosol containers leak to some extent. Gross leakage is readily determinable by a number of well known expedients. The present invention, however is directed to the detection of small leaks. The term "small leaks" herein and in the claims is intended to relate to such leakage rates as would adversely affect a two-year shelf life of the aerosol container. What would constitute such a small leakage rate would depend upon the size of the container and other factors. However, the present invention contemplates detection of leaks which result in a loss of about 10% by weight of propellant per year or less. In the practice of the present invention the lower limit of the size of the leak capable of being detected depends upon the sensitivity of the particular sensing device used. Detection of such leaks is not only difficult by virtue of the fact that the leaks are so small, but also because the detecting frequently has to be done in an ambient atmosphere which contains significant quantities of leaked or spilled propellant as would be found near an aerosol container filling line.
Prior art workers have devised numerous methods and devices for detecting leaks. For example, U.S. Pat. No. 3,302,449, issued Feb. 7, 1967 to J. A. Roberts, teaches a portable leak detector comprising a chamber protected from the ambient air by a curtain of purified air. U.S. Pat. No. 3,729,983, issued May 1, 1973 to M. J. M. Coppens, describes a mass testing apparatus and process providing a plurality of test chambers for the containers to be tested. Each test chamber is evacuated, sealed under low pressure and held to accumulate any leakage from the container therewithin. The accumulated leakage is flushed to an infrared spectra analysis-type detector by a suitable inert gas. U.S. Pat. No. 3,762,212, issued Oct. 2, 1973 to J. D. Morley and P. Forgash, teaches a mass spectrometer leak testing apparatus wherein the container to be tested is placed in a chamber. The chamber is evacuated and the collected leakage is, by vacuum, conveyed to the mass spectrometer. U.S. Pat. No. 3,675,469, issued July 11, 1972 to C. H. Macartney and J. A. Bawduniak, sets forth a direct method for sensing a leak from various parts of an aerosol container. U.S. Pat. No. 3,186,214, issued June 1, 1965 to J. A. Roberts, describes a testing system having a testing chamber into which a leak standard is introduced for calibration purposes. Other leak testing devices and methods are exemplified by U.S. Pat. No. 2,051,758, issued Aug. 18, 1936 to A. A. Trombly; 2,091,323, issued Aug. 31, 1937 to P. Kruse and 2,387,743, issued Oct. 30, 1945 to A. M. Cameron and V. Lelinski.
The present invention is directed to an improved method of detecting small leaks in pressurized containers. The method lends itself well to both continuous and batch-type testing systems. Furthermore, it may be utilized to detect leaks from various parts of pressurized containers as will be described hereinafter.
The test method of the present invention is rapid and accurate in operation; provides means generating a gas leak standard against which each container tested is compared; and provides means for compensating for contamination of the carrier gas and means for compensating for drift of the detector or sensing device.